Wi-Fi and Home Networks
In wireless communications, the IEEE 802.11 family of standards, known as Wi-Fi is a popular protocol for allowing devices to communicate wirelessly using radio wave transmission. A group of devices all communicating via a common wireless access point is known as a wireless local area network (WLANs).
The wireless access point is also commonly combined with a wired network interface for connectivity with wired devices using an Ethernet protocol (IEEE 802.3) and a wide area network (WAN) interface such as an xDSL modem or cable modem for connectivity to remote networks and resources such as file and video servers via an Internet Service Provider (ISP) and then a wide area network such as the Internet. Such devices will be referred to as a hub.
Fairness in Wi-Fi
In the Wi-Fi standards, all devices forming part of a WLAN communicate using a shared radio frequency channel, currently defined to be a frequency in a 2.4 Ghz or 5 Ghz range. Any transmissions by a device will be receivable by other devices within reception range and therefore if two or more devices transmit at the same time, there will be interference. To avoid the need for a transmission scheduler to coordinate all devices, Wi-Fi devices use Carrier Sense Multiple Access-Collision Avoidance (CSMA-CA) to ensure that a device will only try to transmit when they have listened to the transmission channel and determined that the channel is clear. If the channel is in use, then the device will “back off”, i.e., wait a short period of time before trying the channel again. In this way, only one device can transmit on the channel at any given time.
In general, all devices connected to a Wi-Fi network have equal priority. When the channel is deemed to be busy, each device will have similar time-out period before retesting the channel and once acquired, the device has the same opportunity for packet transmission. For example, device A is allowed to transmit 500 packets, and device B is also allowed to transmit 500 packets. Whilst such a scheme provides fairness, if the transmission speed of data packets from device A is much slower than the transmission speed of device B (for example, device A is using a slower transmission scheme for robustness), then device A will lock out the rest of the channel for a much longer period of time, thereby reducing the performance of the network as a whole.
In WLANs, due to the CSMA-CA and fairness policy in Wi-Fi, as the number of connected devices increases, the performance for each individual device connected to the WLAN decreases due to contention for the common channel. At any given time, there is a greater probability that the channel will be in use which will result in any one device having to wait longer before it is able to transmit on the channel.
A large number of visiting devices connecting to a WLAN is problematic for regular users of the WLAN, for example if the main user of a WLAN has visitors and they all connect their personal devices to the WLAN to access network services, then there can be network performance issues for other regular home users of the WLAN. For example, regular users of the WLAN may be subjected to a noticeable drop in performance (for example, slow web page loading times, slow file transfer speeds, dropped video frames and/or bad voice quality) and this can be frustrating.
Quality of Service (QoS)
A device connected to a Wi-Fi network will typically transmit data packets relating to several data applications, for example, file transfer, text, audio, video etc. Each type of application will have different requirements with regards to latency and accuracy. For example the speed of a file transfer is secondary to the requirement for the received data packets to be free of errors and in order. In contrast, for a video streaming application or Voice over Internet Protocol (VoIP) application, dropping packets is preferable to a break in the flow of received and decoded data packets.
To address the different requirements for different services, Quality of Service (QoS) requirements can be defined for the different application types and a packet priority is assigned to packets belonging to each application type. In this way, certain types of traffic to be prioritized for delivery through the network from a sender to a receiver, for example video packets have higher priority than file transfers. This is especially important when there is network congestion.
Whilst QoS provides some control for service prioritization, it is not widely implemented in WLANs. Furthermore, even when QoS is enabled, QoS operates in terms of services and applications, not users. Therefore if visiting users connect their devices to the WLAN and use video streaming or VoIP services, they will receive higher priority than a regular user device downloading a file.